The superabrasive grindstone has low wear compared with conventional grindstones, and is suitable for high-precision shape creating work. On the other hand, because of the difficulty of its truing/dressing, the superabrasive grindstone is presently not in widespread use.
Out of superabrasive grindstones, with respect to a conductive grindstone using metal or the like as a binder, a technique such as discharge truing/dressing or electrolytic dressing is applied (see The Journal of The Society of Grinding Engineers, Vol. 39, No. 5, 1995, SEP, pp. 21-22, and pp. 25-26). However, any conventional method has been a method executed in a liquid, and has been unsuitable for a dry grinding machine, which prevails in the mold manufacturing industry. The aforementioned method has not been simple because it has needed to use a brush to supply power to the main shaft of a grindstone.
In contrast, there is a contact-discharge truing/dressing method wherein a voltage is applied to a pair of electrodes with an insulating grindstone sandwiched therebetween, wherein the electrodes are ground by a conductive grindstone, and wherein a contact-discharge phenomenon occurring at this time is utilized (see The Journal of The Society of Grinding Engineers, Vol. 39, No. 5, 1995, SEP, p. 24). This method is simple because it does not need to use a brush to supply power to the main shaft of a grindstone.
However, in these conventional contact-discharge truing/dressing methods, because the electrodes are ground while keeping constant the depth of cut of the grindstone with respect to the electrodes and the feed speed of the electrodes, no stable contact-discharge phenomena have been achieved, and in some cases, a problem that periodical irregularities have occurred over the circumference of the grindstone working surface has sen (see 1990, The proceedings of The Japan Society for Precision Engineering, Spring Conference, pp. 933-934.) Also, since the electrodes have been ground largely in a mechanical fashion, wear of the electrodes has been heavy. In addition, this contact-discharge truing/dressing method cannot be applied to a nonconductive grindstone.
There are several other truing/dressing methods wherein abrasives are caused to fall off by mechanically shaving away a binder (this is usually a binder other than metal), using a conventional grindstone rotated (see The Journal of The Society of Grinding Engineers, Vol. 39, No. 5, 1995, SEP, pp. 8-11).
However, when being applied to dry grinding, any method has caused a problem in that large quantities of flying abrasives adversely affect the lifetime of a machine tool and human bodies. Moreover, since the truing/dressing according to these methods relies upon a mechanical force, a problem has occurred in that, when attempting to create a sharp V-shaped edge shape, the edge becomes chipped.
In any of the above-described truing/dressing methods, no measures have been taken to conduct truing/dressing while monitoring the circularity of a grindstone. As a result, it has been impossible to continuously and automatically execute the transition of the truing/dressing condition from the rough truing/dressing condition to the finish truing/dressing condition. Furthermore, it has been impossible to determine while conducting truing/dressing, at what point of time the truing/dressing is to be ended.
In addition, in any of the above-described truing/dressing methods, no measures have been taken to conduct truing/dressing while monitoring the decreasing amount of the radius of a grindstone, due to the truing. As a consequence, in in-process truing/dressing, it has been impossible to perform working while correcting the tool path.